Overview and background
By measuring the mass change of the sample under the program temperature control, the thermogravimetric analyzer can effectively analyze the thermal stability and content of different components in the ink. Inks are usually composed of resin binders, pigments, solvents and various additives, among which inorganic fillers such as silica, calcium carbonate, talc, etc. are often added to regulate rheology or reduce costs. The determination of thermal decomposition temperature and inorganic filler content is of practical significance for quality control and formulation optimization.
Test Principle:
During testing, a small sample of ink is placed in a crucible of a thermogravimetric analyzer and heated at a constant rate in a nitrogen or air atmosphere. The curve of the mass with temperature is recorded, known as the TG curve. Different components evaporate, volatilize or decompose at specific temperature ranges, resulting in a stepwise decline in mass. The mass remaining in the high temperature area usually corresponds to inorganic fillers with high thermal stability. The first-order derivative curve DTG can accurately locate the decomposition peak temperature, that is, the thermal decomposition temperature.
Instrumentation and sample preparation
A high-sensitivity thermogravimetric analyzer is selected, with a balance resolution of 0.1 μg and a temperature range of room temperature up to 1000°C. The crucible material is alumina or platinum to avoid reacting with the sample. The ink sample should be thoroughly mixed before testing, and an appropriate amount (usually 10-20 mg) should be laid flat on the bottom of the crucible to reduce the effect of heat transfer gradient. It is recommended to test each sample in parallel three times, taking the mean.
Test conditions and parameters
The following conditions apply to most solvent-based and water-based ink samples:
| Parameter Name | Set value |
| Rate of warming | 10°C/min |
| Temperature range | 30°C to 900°C |
| Atmosphere | Nitrogen, flow rate 50 mL/min |
| Sample quality | Approximately 15 mg |
| Crucible type | Alumina open crucible |
To distinguish between organic coatings and inorganic fillers, the nitrogen flow can be switched to an air atmosphere to burn residual carbon after the nitrogen flow reaches 600°C.
Data analysis methods
Read the weightless step from the TG curve: the first step is usually the release of residual solvent or water, corresponding to about 30-150°C; the second step is mainly the decomposition of the resin matrix, corresponding to 200-450°C; The third step may be the elimination of carbonaceous residues or filler bound water. Inorganic packing content is calculated as a percentage of final residual mass expressed as:
Inorganic packing content = (m900°C / minitial) × 100%
where minitialis the initial mass of the sample, m900°CThe residual mass at 900°C. The thermal decomposition temperature is taken from the temperature value corresponding to the maximum weight loss rate on the DTG curve.
Example of results
The following are typical test results for a black ink in a nitrogen atmosphere, with a table showing the temperature range and mass loss corresponding to each weightless stage:
| Temperature range | Mass loss description |
| 30-150°C | The loss is about 2%, which is residual solvent and moisture |
| 150-400°C | The loss is about 68%, which is the decomposition of resin and organic pigments |
| 400-600°C | The loss is about 12%, which is the slow decomposition of carbonaceous residues |
| 600-900°C | The residue is about 18%, which is inorganic filler and a small amount of ash |
The calculated value of the inorganic packing content in this sample was 18% (based on 900°C residue), and the thermal decomposition temperature was determined by the DTG curve to be 358°C.
Influencing factors and precautions
The heating rate will affect the decomposition temperature measurement, and too fast a rate will cause temperature lag, and it is recommended to control it no more than 20°C/min. Too large a sample volume may cause uneven internal temperature, so it is advisable to lay it in a thin layer. The type of ink should be considered in the selection of atmosphere: volatilization and decomposition can be distinguished in nitrogen, and the air atmosphere can promote complete combustion, but may obscure part of the decomposition step. The crucible needs to be dried in advance to avoid moisture adsorption.
Frequently Asked Questions and Countermeasures
| Problem phenomenon | Countermeasures |
| The curve rises | Check whether the crucible is clean or static, and whether the sample volume is too large |
| The decomposition steps are not clear | Reduce the rate of warming or increase the sample volume |
| The residual mass is abnormally low | Check if the sample is carried away by splashing or strong air currents |
| Poor reproducibility | Stir well before sampling to ensure uniformity |
Application value
This method can quickly evaluate the thermal stability of inks in the printing curing process and provide a quantitative basis for the proportion of inorganic fillers in the formulation. By adjusting the type and content of fillers, the rheological properties and film-forming hardness of inks can be improved while controlling costs. Relevant studies also showed that packing materials with different particle sizes would cause a slight deviation in the decomposition temperature, which needed to be analyzed in conjunction with the specific system.
Cited material
1. Application of Thermal Analysis in Printing Ink Characterization, Journal of Coatings and Ink Technology, Issue 3, 2021.
2. Quantitative Methods for Thermogravimetric Analysis in Organic-Inorganic Composites, Technical Handbook of Materials Testing, 2nd Edition.
3. Standard Operating Procedures for Thermogravimetric Determination of Inorganic Fillers in Inks, Compilation of Industry Technical Specifications, 2023.